Over the years, various microelectromechanical systems ("MEMS") have arisen which require the necessity to sense temperature, pressure, strain, acceleration, rotation, infrared radiation, chemical properties of liquids and gases, and other physical inputs. Accordingly, various types of microsensors have been developed which receive analog and digital electrical inputs and also sense or measure these other physical inputs, e.g., acceleration, pressure, temperature, strain.
Integrated circuits are widely used in many of these MEMS or electronic applications. Various integrated circuit manufacturing processes, e.g., very large scale integrated ("VLSI"), are also widely known and provide various advantages. The complimentary metal oxide semiconductor ("CMOS") manufacturing technology, for example, generally provides a low power dissipation advantage over known metal oxide semiconductor ("MOS") processes. Microsensor manufacturing which is compatible with known integrated circuit manufacturing processes, however, can be quite complicated, especially because of a need for integrating various types of structures at relatively low cost.
Some types of well known thermosensors, for example, are thermistors and thermocouples for measuring the temperature of a surrounding environment. Thermistors and resistive temperature detectors ("RTDs") are primarily based on the concept of change of mobility and carrier density with temperature. These changes are often represented by temperature coefficients that may be constants or nonlinear functions of temperature. Because resistance of a thermistor is generally an exponential function, linearization networks are often used to make the output of a thermistor a linear function over a desired range. These linearization networks, however, often require the sacrifice of sensitivity.
A thermocouple, on the other hand, is generally based on a thermoelectric effect known as the Seebeck effect. Two different metals are usually joined at one point to form a thermocouple. Various metals, for example, can be used for various temperature ranges and sensitivity. Semiconductors can also be used with a metal to form a microthermocouple. The two materials are conventionally joined together at one end, e.g., a sensing junction, and terminated at their other ends in such a manner that the terminals, e.g., a reference junction, are both at the same and known temperature, e.g., a reference temperature. The leads from the reference junction are connected to a load resistance to complete the thermocouple circuit. Due to the Seebeck effect, a current is caused to flow through the circuit whenever the sensing junction and the reference junction are at different temperatures. Often in practice, for example, the reference junction is either held at a known constant temperature or is electrically compensated for variations in a preselected temperature.
Both the thermistor and the thermocouple, however, produce analog outputs which often are not readily compatible with associated detection circuitry or logic circuitry. Also, processing or detecting circuitry can increase overhead and costs associated with producing a microsensor, and especially an integrated sensor.